The invention relates to a method of loading adsorbent into chromatographic columns used in small to medium scale separations of chemicals such as chiral chemicals and pharmaceuticals.
Chromatographic separation is a highly useful method of separating a mixture of two or more compounds which are not readily separated by other means such as fractional distillation. During a chromatographic separation this mixture is injected into a bed of an adsorbent or stationary phase. This material is chosen for its ability to selectively retain one of the compounds more strongly than the other. A continuous stream of a fluid referred to as the solvent or mobile phase is slowly passed through the bed, and the less strongly retained compounds(s) gradually moves through the bed faster than the other compound(s). This gradually forms two or more xe2x80x9cpeaksxe2x80x9d, each having a higher concentration of the respective compound(s) and which are withdrawn separately.
These separations are promoted by long beds of adsorbent which are free from voids and packing irregularities which would tend to cause backmixing of the fluids flowing through the bed. The method used to pack the adsorbent into the long tubes used to perform the separation is important, and the importance increases as the diameter of the tube is increased to accommodate higher fluid rates needed for higher capacity separations.
U.S. Pat. No. 5,013,433 issued to Y. Shalon describes a chromatographic column characterized as having a zero void volume. The invention centers upon the construction of the distribution and collection devices located at the ends of the column for assuring uniform flow of the liquid through the column.
U.S. Pat. No. 5,169,522 issued to Y. Shalon et al. describes a hydraulically active liquid chromatography column suitable for use in HPLC systems. A cylindrical bed of adsorbent is retained within an adsorbent chamber and is compressed by a piston driven by a hydraulic fluid in the hydraulic chamber. An opening is provided in the end plate of the apparatus for enabling the monitoring, maintaining and releasing of the pressure in the column as necessary. This opening may be equipped with a gauge and valve.
An article by Yehuda Shalon printed in the magazine American Laboratory in September 1997 describes problems encountered in loading chromatographic columns including packed columns. FIG. 2 of the article illustrates a spring-loaded HPLC column said to reduce these problems. The piston applying pressure to the cylindrical bed of adsorbent may be driven downward through a threaded screw at an upper end of the column. A compressed spring intermediate the piston and the threaded screw acts directly on the piston. The spring maintains a relatively constant pressure upon the bed of adsorbent.
U.S. Pat. No. 5,866,008 issued to Y. Shalon et al. describes an apparatus and method for loading high-pressure chromatographic columns. In column 10, it is stated the slurry medium can be agitated before compression by rocking the column about rotating joint 42.
The invention is a method to densely load adsorbent into small adsorptive separation columns used in performing high-pressure liquid chromatographic separations. The invention includes a step in which the adsorbent is fluidized to remove irregularities and voids from the adsorbent bed while the adsorbent is being loaded into the column or after it is in the column.
One broad embodiment of the invention may be characterized as a method for loading a particulate adsorbent into a column used for chromatographic separation comprising placing a quantity of adsorbent into a cylindrical column; fluidizing the adsorbent by the upward passage of a liquid through the column, and compressing the adsorbent by use of a piston located within the column.